1. Field of the Invention
The present invention relates to a Talbot interferometer, its adjustment method, and a measurement method.
2. Description of the Related Art
A Talbot interferometer can be used to measure a (transmission or reflection) wavefront of light that has passed a test object (a test optical system or a test optical element). Mitsuo Takeda et al., “Lateral Aberration Measurement Using A Digital Talbot Interferometer,” United States, Applied Optics, vol. 23, no. 11, pp. 1760-1764 (1984). For improved measurement accuracy, an arrangement of the diffraction grating and the image pickup device needs to satisfy a condition referred to as a Talbot condition.
Although the diffraction grating and the image pickup device are arranged at design positions in the conventional Talbot interferometer, the design positions can shift from the Talbot condition due to alignment errors, and the measured wavefront contains an error.